I think it can be worded similiar to Witch's Major Lesson:
Major Lesson wrote:
Special You can select this feat a second time if you’re 14th level or higher, and a third time if you’re 18th level or higher. Choose a different lesson each time.
I'm entirely agree with you that evolution feats should have at least 25, but having the Summoner's feat page with that number will eclipses non Evolution feats. Structuring it to lesson-like will also made it easier for Paizo writing additional,thematic evolutions in supplemental sourcebook, e.g. the Animal Companion Elemental Specialization / Baba Yaga lessons from LO: Legends.